For example, a master cylinder for a vehicle includes a cylinder main body having a cylinder bore, a piston that defines a hydraulic chamber in the cylinder bore of the cylinder main body, and a spring device that provides the piston with the force of the spring. The elements of the spring device are a retainer member that restricts the expansion/compression of the spring, and the spring supported by the retainer member.
In most spring devices, the piston itself serves as a direct spring bearing for the spring, and therefore the spring device itself is not formed as a unit and cannot be handled independently. Various examples of such conventional, non-unitized devices are disclosed by the following documents.
Patent Document 1: Japanese Patent No. 3035228 that discloses a spring device including a cup-shaped retainer, a screw member that has its one end coupled to the retainer and its other end supported by a piston, and a spring supported between the retainer and the piston (see FIG. 1 in particular).
Patent Document 2: U.S. Pat. No. 5,111,661 (that corresponds to Japanese Patent Laid-Open No. H03-109164) according to which an extended part of the piston plays the role of the spring member in the disclosure of Japanese Patent No. 3035228 described above (see the part denoted by reference numeral 42 in FIG. 1 in particular).
Patent Document 3: Japanese National Publication No. 2002-535200 (that corresponds to Intentional Publication WO 00/44600) that discloses a spring device having a retainer arrangement in which a sleeve-shaped retainer member is coupled with a pin-shaped retainer member in a transverse direction deviated from the axial line, and a piston (26) serves as a spring bearing for a spring (38) (see FIG. 1 in particular)
Meanwhile, there is a known unitized spring device including a pair of coupled retainer members whose axial length is extensible/contractible, and a spring supported by these retainer members, and these elements can be handled independently as a unit.
Patent Document 4: Japanese Utility Model Publication No. H05-13666 discloses a spring device that includes a cup-shaped retainer, a rod member having its one end coupled to the retainer and its other end having a spring bearing portion, and a spring supported between the spring bearing portion of the rod member and the retainer (see FIG. 3 in particular). The spring device formed as a unit that can be handled independently is more advantageous when it is assembled to the cylinder main body than those that are not formed as a unit.